Jet mill

ABSTRACT

The improvement relates to the heater of compressed gas which is delivered from the heater to the nozzles of a jet mill, the flow of compressed gas escaping from the nozzles drawing in and accelerating the particles of the material being comminuted. The improvement consists in that each nozzle of the jet mill communicates by way of the inlet thereof with a chamber housing a heater element. The chambers communicate with a source of compressed gas supply. Compressed gas is delivered to the nozzles through a chamber housing a heater element.

United States Patent [191 Gorobets et al.

[ 1 JET MILL [76] Inventors: Vladimir Ivanovich Gorobets; LarisaZhanovna Gorobets, both of ulitsa Sevastopolskaya. 26a, kv. 5; AnatolyAlexandrovich Ivanov, prospekt K. Marxa 13/15, kv. 29; Georgy PetrovichTropin, ulitsa Bazhova 28, kv. 10, all of Dnepropetrovsk; VeniaminIvanovich Chirkov, ulitsa Planetnaya l4, kv. 28, Moscow; VeniaminViktorovich Konstantinov, ulitsa Fadeeva 59, kv. 70, Volgograd; ViktorDeomidovich Belyaev, ulitsa Kaverina, 14, kv. 1, Dnepropetrovsk, all ofUSSR.

[22] Filed: May 30, 1973 [21] Appl. No.: 365,179

[52] US. Cl. 241/39; 241/79.1; 241/80 [51] Int. Cl. B02c 19/06 [58]Field of Search 241/39, 79.1, 80; 219/382 [56] References Cited UNITEDSTATES PATENTS 725.450 4/1903 Keller 219/382 1 Apr. 15, 1975 1935.34411/1933 Andrews et al 241/39 2.297.726 10/1942 Stephanoff 241/392.932.458 4/1960 Croft et al. 241/80 X 3,244,860 4/1966 Lindley 219/382X FOREIGN PATENTS OR APPLICATIONS 846,114 8/1960 United Kingdom 219/382Primary Examiner-Granvi1le Y. Custer, .lr. Assistant E.raminerCraig R.Feinberg Attorney, Agent, or Firm-Holman & Stern [57] ABSTRACT Theimprovement relates to the heater of compressed gas which is deliveredfrom the heater to the nozzles of ajet mill, the flow of compressed gasescaping from the nozzles drawing in and accelerating the particles ofthe material being comminuted. The improvement consists in that eachnozzle of the jet mill communicates by way of the inlet thereof with achamber housing a heater element. The chambers communicate with a sourceof compressed gas supply. Compressed gas is delivered to the nozzlesthrough a chamber housing a heater element.

4 Claims, 3 Drawing Figures JET MILL BACKGROUND OF THE INVENTION Theinvention relates generally to grinding equipment and more particularlyto jet mills. wherein the material is ground through the collision ofthe particles thereof accelerated by the jets of compressed gas or vaporforced through the nozzles.

At present jet mills have gained wide acceptance.

It is common knowledge that the main working component of a jet mill isa milling chamber with built-in injectors which draw in. accelerate anddeliver the par ticles of the material to be ground to the millingchamber.

Jet mills also incorporate a classifier for sizing the particles of thematerial in the course of grinding. a precipitator separating the groundparticles of the material from the stream of exhaust gas, as well as anexhaust device venting the exhaust gas from the mill after the gas hasbeen stripped of the comminuted material.

The compressed gas which forms the working flow accelerating theparticles of the material being comminuted is supplied to the injectornozzles from a compressed gas source. such as a low-pressure compressoror a compressed gas vessel.

The working flow in jet mills is frequently formed by the exhaust vaporfrom heat and electric power plants delivered through special pipelines.In such a case the heat and electric power plant itself is the source ofthe working medium.

Besides. those skilled in the art know of a jet mill which employs fuelcombustion chambers as the source of compressed gas the chambers beingintegral components of the mill and communicating with the nozzles ofthe injectors (see. for example. U.S.S.R. Authors Certificate No.314.545. Cl. 802C 1906). Naturally. in this case the products of fuelcombustion constitute the medium which forms the working jet.

However. the jet mills using heat and electric power plants orcompressor units as their source of compressed gas feature a seriousdrawback which consists in their excessive power consumption caused bythe need to ensure a high compression ratio of the gas, since in thiscase the particles are accelerated primarily by the potential energy ofa comparatively lowtemperature compressed gas whose heat energy isinsufficient for particle acceleration. Another disadvantage of the jetmills employing vapor as the working medium is the fast rate of wear ofthe mill parts due to the high corrosivity of vapor.

Among the disadvantages of the jet mills employing the products of fuelcombustion as their source of compressed gas note the fast rate of wearof the equipment due to the high corrosivity of the fuel combustionproducts. the difficulties involved in the temperature control. the needfor on-site fuel stocks and the pollution of the atmosphere with thecombustion products.

SUMMARY OF THE INVENTION It is an object of the present invention toobviate or mitigate the foregoing diadvantages of the known jet mills.

The primary object of the invention is to improve the system of heatsupply to the compressed gas so as to avoid the need for fuel combustionbut without raising the compression ratio of the gas forming the workinget.

Other objects of the invention are to avoid using corrosive workingmedia. such as combustion products or vapor. prolong the useful life ofthe jet mills. simplify maintenance. rule out the need to have fuelstocks and eliminate the menace of air pollution with the combustionproducts.

The present invention contemplates improving the system of heat supplyto the compressed gas so as to avoid the need for fuel combustion butwithout raising the compression ratio of the gas forming the working et.

Accordingly there is provided a jet mill in which the material is groundthrough the collision of its particles accelerated and delivered to themilling zone by the jets which are formed as compressed gas is fedthrough the nozzles. wherein, in accordance with the invention, eachnozzle communicates by way of the inlet thereof with a chamber housing aheater element and communicating with a source of compressed gas supply.

In order to improve the efficiency of heat exchange between the gas andthe heater element, as well as to prolong the useful life of the heaterelement. the latter should be preferably placed inside the chamber in aperforated sleeve, whereof one end is connected to the nozzle, while theother end of the sleeve should communicate with the cavity of thechamber. and the pipe supplying compressed gas is built into the sectionof the chamber opposite that where the sleeve end communicating with thechamber cavity is disposed.

With the foregoing embodiment of the chamber. the bulk of compressed gassupplied thereinto is delivered to the heater element through the openend of the sleeve. with the inner walls of the chamber being exposed tothe flow of cold gas. This will permit avoiding the need to constructthe chamber walls from a hightemperature material and will additionallyminimize heat losses through the chamber walls.

A part of the compressed gas delivered into the chamber will penetrateinto the sleeve of the heater element through the perforations in thesleeve walls. The gas inflow penetrating into the sleeve through theperforations in its walls will decelerate the main flow inside thejacket, thereby raising the efficiency of heat exchange between thecompressed gas being heated and the heater element. Furthermore. withthe slowingdown of the main flow. the rate of corrosion of the heaterelement is reduced resulting in its lower rate of wear.

Another design of an air-pressure mill is possible, ac-

cording to which the perforated sleeve itself is a heater element. Inthis case the heat exchange in the chamber housing the heater element isintensified. However. with the heater element removed from inside thesleeve. the aerodynamic drag is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of the present inventionwill now be described in detail. by way of example, with reference tothe accompanying drawings. wherein:

FIG. 1 is a schematically illustrated elevation view of a jet mill inaccordance with the invention;

FIG. 2 is a preferred embodiment of a chamber housing a heater elementenclosed in a perforated jacket; and

FIG. 3 is another embodiment of a chamber with a heater element formedas a perforated sleeve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The jet mill of thisinvention incorporates a milling chamber 1 (FIG. 1) with injectors 2,whereof nozzles 3 communicate by way of the inlets thereof with chambers4 housing electric heater elements 5 supplied from a current supplysource 6. The chambers 4 communicate via pipes 7 with a source (notshown) of compressed gas supply. a low-pressure compressor or acompressed gas vessel. Along with the nozzle 3., the injector alsoincorporates a mixing sleeve 8. The nozzles 3 are disposed inside inletchambers 9 for the material to be ground. The inlet chambers 9communicate via pipes 10 with a feed hopper I1 and are disposed adjacentthe entrance port 12 of the mixing sleeves 8.

The jet mill also incorporates a comminuted material classifier 13 whichcommunicates via a pipe 14 with the milling chamber 1 and via pipes 15with the corresponding inlet chambers 9. The outlet of the classifier I3is connected with a precipitator 16 serving to separate the comminutedmaterial from the gas stream.

The precipitator 16 is coupled to an exhaust device 17 venting theexhaust gas from the mill.

In order to improve the efficiency of heat exchange between the heaterelement and the gas to be heated. and also to prolong the useful life ofthe heater element. the chamber housing the heater element should bepreferably constructed as described hereinafter with reference to FIG.2.

A heater element 18 (FIG. 2) is disposed inside a chamber 19 in a sleeve20 with perforations 21. The sleeve 20 communicates by way of one endthereof with the nozzle 3 of the injector 2. By way of its other. open.end the sleeve 20 communicates with the cavity of the chamber 19. A pipe22 is built into the chamber 19 to supply compressed gas. the pipe 22being disposed in that section of the chamber 19 which is opposite thesection where the end of the sleeve 20 communicating with the chambercavity is disposed.

The mill operates in the following manner. Compressed gas is suppliedvia the pipes 7 to the chamber 4 (FIG. I) or I8 (FIG. 2) and is heatedin flowing around the heater element 5.

In the other embodiment. the compressed gas is supplied to the chamber19 through the pipe 22 and flows in the chamber as indicated by thearrows. The bulk of gas passes in the space between the walls of thechamber 19 and the sleeve 20 and enters the sleeve 20 through the openend thereof. A smaller portion of the heated gas finds its way into thesleeve 20 through the perforations 21. Such a pattern of compressed gastransfer in the chamber 19 provides for the most efficient heat exchangebetween the gas and the heater element l8, safeguards the walls of thechamber 19 against overheating and accordingly reduces the amount ofheat losses through the walls of the chamber 19. The gas flows enteringthe sleeve 20 through the apertures 21 decelerate the main compressedgas flow through the open end of the sleeve 20, thereby improving theefficiency of the heat exchange and slowing down the rate of corrosionof the heater element surface.

The entire mass of gas is delivered from the sleeve 20 to the nozzles 3,expands therein and escapes therefrom to the mixing sleeves 8 at a highvelocity. During this process the material to be ground is drawn in fromthe inlet chambers 9 by the high-speed gas jet escaping from the nozzles3 and. entering the mixing sleeves 8, acquires a velocity equal or closeto that of the gas. Supplied at a high velocity to the milling chamber1, the particles of the material collide with one another and with thewalls of the milling chamber 1, thereby being ground.

Having lost their speed. the particles are swept by the gas stream viathe pipe 14 to the classifier 13 where they are sized. The oversize isreturned via the pipes 15 to the inlet chambers 9, mixed therein withthe starting material. whereupon it is recycled. The particlescomminuted to a required size are carried by the gas stream .to theprecipitator 16, where they are precipitated and discharged through abin 23. The gas flow stripped of the particles of the comminutedmaterial is vented by the exhaust device to the atmosphere.

In case the heater element is formed as a sleeve 20a (FIG. 3) withperforations 21, the pattern of compressed gas transfer inside thechamber I9 is unaffected for all practical purposes. but the heatexchange between the compressed gas heated in the chamber I9 and thesleeve 20a serving as the heater element is intensified to the utmost.

We claim:

1. A jet mill. wherein the material to be comminuted is ground throughthe collision of its particles accelerated by gas jets. comprising: amilling chamber; nozzles being disposed within said chamber and havingoutlets thereof directed toward the interior of said chamber; additionalchambers communicating via pipes with a source of compressed gas andbeing connected directly to said nozzles; heater elements being disposedin said additional chambers; a classifier sizing the particles andcommunicating via pipes with said milling chamber; a precipitator beingdisposed downstream of said classifier and communicating therewith; anexhaust device being disposed downstream of said precipitator andventing exhaust gas from the mill; and a feed hopper communicating withsaid milling chamber at the points where said nozzles are disposedtherein.

2. A jet mill as claimed in claim 1, wherein each of said additionalchambers communicating with the source of compressed gas houses aperforated sleeve associated with each heater element; each said sleevecommunicating at one end thereof with the corresponding nozzle and atthe other end with the chamber housing the sleeve; and wherein pipes.whereby said additional chambers communicate with said sources ofcompressed gas. are built into that section of said additional chamberswhich is opposite the section where said sleeve communicates with saidchamber and adjacent the associated nozzle.

3. A jet mill as claimed in claim 2, wherein each said sleeve is theheater element.

4. A jet mill as claimed in claim 2, wherein each said sleeve enclosesthe associated heater element.

1. A jet mill, wherein the material to be comminuted is ground throughthe collision of its particles accelerated by gas jets, comprising: amilling chamber; nozzles being disposed within said chamber and havingoutlets thereof directed toward the interior of said chamber; additionalchambers communicating via pipes with a source of compressed gas andbeing connected directly to said nozzles; heater elements being disposedin said additional chambers; a classifier sizing the particles andcommunicating via pipes with said milling chamber; a precipitator beingdisposed downstream of said classifier and communicating therewith; anexhaust device being disposed downstream of said precipitator andventing exhaust gas from the mill; and a feed hopper communicating withsaid milling chamber at the points where said nozzles are disposedtherein.
 2. A jet mill as claimed in claim 1, wherein each of saidadditional chambers communicating with the source of compressed gashouses a perforated sleeve associated with each heater element; eachsaid sleeve communicating at one end thereof with the correspondingnozzle and at the other end with the chamber housing the sleeve; andwherein pipes, whereby said additional chambers communicate with saidsources of compressed gas, are built into that section of saidadditional chambers which is opposite the section where said sleevecommunicates with said chamber and adjacent the associated nozzle.
 3. Ajet mill as claimed in claim 2, wherein each said sleeve is the heaterelement.
 4. A jet mill as claimed in claim 2, wherein each said sleeveencloses the associated heater element.